It was shown that by the classical pathway of complement activation, it is possible to kill HIV-1 infected cells. It was found that fresh sera of Rabbit showed a dose dependent viral inactivating property against cell free HIV-1. Further in the present project, it is possible to elucidate the mechanism to understand the lack of activity of human serum against HIV-1. With the same idea, presently the work is ongoing to test a panel of HIV-2 sera for their ability to activate human complement by the classical pathway mediated Membrane Attack Complex System (MACS). Activation is being assessed by the C3-complement component deposition using anti C3 conjugated to FITC. Analysis of complement mediated cytolysis of infected cells using serum samples against recombinant HIV-1 env or core antigens speculates that env gp160/120 and gag p24 acts as target antigens for antibody and complement mediated cytolysis.